Is Having a Transmission With More Gears Really Better?

The new Ford Mustang is offered with a 10-speed automatic transmission, and so is the new F-150 and Lexus LC500.

Other crossovers like the Jeep Renegade, Fiat 500X, and Jeep Compass sport nine-speed automatic transmissions as well, but what’s the advantage of having more gears in your transmission, and what’s the limit? Is having more gears really better?